- LR-R and LR-S: Patients receive medium-high-dose (mHD) methotrexate IV over 24 hours on days 50, 64, and 78; etoposide phosphate IV over 1-2 hours and cytarabine IV over 1 hour on day 66; oral mercaptopurine on days 50-56 and 78-120; oral thioguanine on days 64-70; and methotrexate IT on days 29, 50, 64, and 78. Patients in LR-S group who still have a detectable MRD load on day 29 are randomized (randomization 1) to 1 of 2 arms to receive cytarabine and pegaspargase vs. clofarabine and pegaspargase.